Dehydration of hydrogen chloridehydrocarbon mixtures by distillation



" Patented Mai'. l, 1949 PATENT oFFloE DHYDRA'EIN OF HYDROGEN CHLORIDE- HYDRUCABBON mTUBES BY DISTIL- LATION .lohn W. Latchum, Jr., Bartlesville, Okla., assignor to Phillips Petroleum Company, a corporation of `Delaware application January s, 1944, semaine. 16,883

from such mixtures obtained in the isomerization of normal butane to isobutane by means of aluminum chloride in the presence of hydrogen chloride. Still more particularly it relates to the removal of water concomitantly with the fractionation of the isomerization eiiluent to recover the hydrogen chloride contained therein for recycle to the reaction zone. l

The principal object of the present invention is to provide a, methodfor separating water from hydrogen chloride-hydrocarbon mixtures, Another object is to provide such a method for removing water from concentrated hydrogen chloride-hydrocarbon mixtures. Another object is to provide such a'method which effects removal of .water in conjunction with the fractionation to recover a recycle hydrogen chloride stream containing the hydrogen chloride in admixture with hydrocarbons comprising chiefly propane and lighter. Another object is to provide a method of the foregoing type wherein the hydrogen chloride content of the` recycle stream is greater than 65 per cent by weight of HC1. Another object is to provide a method of the foregoing type which involves a minimum .of additional expense and which eiiects a substantially complete removal of water from the recycle concentrated hydrogen chloride stream. Numerous other objects will hereinafter appear.

In hydrocarbon conversion processes using aluminum chloride .as the catalyst, great care is used in keeping moisture from the catalyst. num chloride forms a hydrocarbon-aluminum chloride complex sludge Which soon becomes inactive thereby rendering expensive aluminum chloride useless. The less sludge formed in a hydrocarbon conversion process of this type," the greater the activity and the longer the life of the catalyst and moreover the lower the chemical cost of the process. As moisture comes in contact with the catalyst hydrogen chloride is formed and the formation of sludge is increased.

When normal butane is isomerized to isobutane, aluminum chloride and hydrogen chloride Alumia claims." (ci. 2oz-lss) 4the secondarychamber is then passed through any suitable means for removing volatilized aluminum chloride therefrom, as for example, through a guard chamber packed with Porocel .or equivalent adsorbent or, more preferably,

through la scrubbing tower countercurrently to concentrated sulfuric acid. In this way aluminum chloride is removed from the emuent vapors before they are passed into the rst fractionator wherein hydrogen chloride is removed for recycle. The hydrogen chloride is removed in admixture with hydrocarbons which typically would contain about 60 per cent methane, 3 per cent ethane, 25 per cent propane and a balance of about 12 per cent ofV butanes. Some hydrogen may also be present. The recycle strearnusually contains more than 65 per cent of hydrogen chloride, the balance being hydrocarbon and water.

Moisture may be present in objectionable amounts inthe isomerization of normal butane in accordance with'the foregoing even though precautions have been taken to keep moisture from within the system. This moisture may have enteredthe hydrocarbon stream -by being desorbed from the Porocel or equivalent adsorbent contained in the secondary chamber, from incomplete drying of the feed, from the use of sulfuric acid which contains more than 15 per cent water in the scrubbing step, from opening the system to the atmosphere for charging catalysts, or repairing, from the backing up of aqueous solution from the caustic wash through which the kettle product from the rst or HC1 fractionator passes prior to entry into theusual isobutane fractionation system, or by other means. Various methods have been used to remove and keep moisture from the recycle streams, but in spite of all precautions moisture appears in the system from time to time.

In accordance with the present invention practically all of the moisture which enters the HC1 As pointed out above, hydrogen .chloride recycle may be used to catalyze the reaction. In a typical process the normal bu'tane and hydrogen chloride are dried, contacted with aluminum chloride in a primary reaction chamber and -passed thence r r into a secondary chamber which contains Porocel or other adsorbent upon which the aluminum chloride contained in the eiliuent from the primary chamber is deposited. The eluent from is separated in this fractionating 4column from the heavier hydrocarbons. This hydrogen chloride together with hydrocarbons as mentioned above and occasionally hydrogen, along with most of the water contained in the feed to this fractionator, is removed as an overhead product. In conventional practice this overhead product is at least partially condensed and at least part ofthe condensate is returned to the top of the HC1 fracy tionator as reflux, the balance of the overhead 4constituting the recycle stream.

. liquid condensate.

the trap may be periodically or continuously drocarbon mixture in the condensate accumu lator or at some other convenient point. In the practice ofthe present invention a water trap may be placedl in the line through which the reux returns from the partial condenser to the top of the HC1 fractionator or at\any other point in the lines or vessels carrying orY containing the The lwater'which settles in drained from the liquid condensate by means of this trap.

The process of the present invention, in its broader aspect, involves eecting removal of water from a' vaporized mixture containing hydrocarbons, hydrogen chloride andwater by at least partially condensing the mixture, allowing the condensate to separateainto a hydrocarbon- Y lwdrogen chloride layer and an aqueous layer, -and separating these layers Preferably sufficient of the mixture is condensed that substantially all or all of the water is4 condensed. Often the entire mixture is condensed. The `vaporized rous hydrogen chloride-hydrocarbon-water mixture. The hydrocarbon-hydrogen chloride phase Y separated as above is substantially free of water,

usually containing notv over 0.2 per cent by weight of water.

In a more specific aspect the present invention involves passingv a feed containing hydrogen chloride, light hydrocarbons, heavier hydrocarbons,'and an objectionable amount of water into a fractionating zone wherein the hydrogen chloride, most of the water, and the light hydrocarbons are substantially completely separated from the heavy hydrocarbons, at least partially condensing this overhead of hydrogen chloride and hydrocarbons comprising mainly three carbon atoms, and lighter hydrocarbons allowing the condensate to separate intotwo layers, an upper layer of hydrogen chloride and hydrocarbons practically free from water and a lower layer which is aqueous, and withdrawing this aqueous layer. refluxed with the necessary amount of the hydrogen chloride-hydrocarbon phase.

Preferably the invention is` applied to the eilluent from the isomerization of normal butane by means of aluminum chloride and 'hydrogen chloride. Preferably this eluent has been' freed from vaporized AlCla. In such case the reaction eilluent and feed to the HC1 fractionator consists essentially of hydrogen chloride, propane and lighter hydrocarbons, and C4 hydrocarbons consisting of normal butane and isobutane, together with such water as has been backed up in the system or was present in the original feed. This eilluent is fractionally distilled in the HC1 fractionator to separate substantially all of the normal butane and isobutane as a bottom product in admixture with .any heavier hydrocarbons which may be inevitably formed in the reaction. The overhead from this HC1 fractionator consists essentially of hydrogen chloride, Ca and lighter hydrocarbons and most of the water in.

the fractionator feed. The overhead is at least partially condensed. This condensation effects liquefaction of practically all of the waterl and of a substantial portion of the HC1 and hydrocar- The top of the column is usually layer comprises water saturated with respect to moved via line II.

hydrogen chloride. These two layers are separately withdrawn. At least a portion of the upper layer is passed as reflux to the top oi' HCl fractionator. Any balance of the upper layer together with any uncondensed overhead is passed as recycle to the isomerization unit. The withdrawn aqueous layer may be discarded where it amounts to onlya few gallons a day. If desired, the aqueous layer may be passed to a suitable concentrating means for recovering anhydrous HC1 therefrom. This aqueous layer is saturated with hydrogen chloride at` the pressure prevailing and so may contain up to about 67 per cent hydrogen chloride by weight.

'The invention is preferably applied to those HCl-hydrocarbon-water mixtures in vaporous form which contain such an amount -of hydrogen chloride with respect to water as would give more than 67 percent of HCl by weight based on the weight of HC1 and water only. Usually the amount of water is so small that the hydrogenv chloride is present in amount at least equal to per cent by weight based on the weight of hydrogen chloride and -water taken vby themselves.

When normal butane is being isomerized, the fractionating column in which the hydrogen chloride is separated may operate witha kettle temperature of 20o-300 F., more preferably about 235 F., and overhead temperature of 75-150 F., more preferably 100 F., and 350-450 pounds per square inch pressure, more preferably 400 pounds per square inch.v

Referring to the drawing, n-butane feed enters via line I, is preheated in 2 and fed via line 4, in admixture with recycle HC1 entering via line 5, to reactor 6, the operation of which forms no part of this invention. The eiiluent, usually vaporous, passes via line l to AlCla-removal means 8 of any suitable type. The efiluent is condensed and pumped via line 9 to HCl fractionator I0, whence a bottoms product containing substantially all or all of the C4 hydrocarbons and any heavier is re- The overhead is removed via line I2, partially or completely condensed in condenser I3 and the liquid is passed to any suitable layer separation means I4 lin which the layer formation takes place. The lower water layer is drawn off via line I5. The upper layer is at least in part passed via line I6 to the top of column I0 as reflux. Any uncondensed `overhead in admixturewith any balance of the upper layer are recycled via" lines I1 and 5.

To charge the-reactor 6with aluminum chloride, the hot feed may be passed through AlCla sublimer I8, the recycle in line 5 being preferably discontinued during this operation.

In some cases, depending upon the pressure, temperature and proportions of hydrogen chloride and hydrocarbon relativeto one another in the vaporized mixture and irrespective of the Water content, three layers may form, one being hydrocarbon containing dissolved HCl and water, the second being hydrogen chloride containing .dissolved water and hydrocarbon, and the third being water containing dissolved hydrogen chloride and hydrocarbons In such case the hydrocarbon layer will be employed as the reflux for column I unless it is insliicient in amount in which event it will be supplemented by at least a portion of the hydrogen chloride layer to give the required amount of reflux.

From the foregoing it Will be seen that the present invention involves a simple, unique and advantageous means of recovering water from vaporized hydrogen chloride-hydrocarbon mixtures, especially from the overhead from a HC1 fractionator operating on the eliiuent from the isomerization of normal butane. Numerous other advantages of the process of the present invention will be apparent to those skilled in the art.

While the foregoing description gives certain details as to the preferred mode of. operation and illustrates the process as applied to the isomerization of normal butarie, it is to be understood that the invention is not limited to the illustrative details given but is to be taken as limited only ing hydrogen chloride in excess of 67v per cent of the weight of hydrogen chloride and water, withdrawing a bottoms product containing normal butane, isobutane and any heavier hydrocarbons present, at least partially condensing said overhead, allowing the condensate to separate into two liquid layers, namely, a hydrocarbon-hydrogen chloride layer substantially free from water and an aqueous layer composed of water saturated with hydrogen chloride, .separately withdrawing the layers and recycling the substantially anhydrous hydrocarbon-hydrogen chloride layer to the isomerization zone.

2. In a process for the isomerization of normal butane in the presence of aluminum chloride and -hydrogen chloride wherein the aluminum chloride free effluent from the isomerization reaction c cntains hydrogen chloride, propane and lighter hydrocarbons,.normal butane, isobutane and water, that improvement which comprises passing said aluminum chloride free eilluent into a fractional distillation column and therein fractionl. ally distilling the same, withdrawing an overhead containing hydrogen chloride, propane, lighter hydrocarbons and Water, said overhead containing hydrogen chloride in excess of 67 per cent of the weight of hydrogen chloride and water, withdrawing a bottoms product containing normal butane, isobutane and any heavier hydrocarbons present, at least, partially condensing said overhead, allowing the condensate to separate into two liquid layers, namely, a hydrocarbonhydrogen chloride layer substantially free from water and an aqueous layer composed of water saturated with hydrogen chloride, separately withdrawing the layers.'reuxing the top of the column with a portion of said hydrocarbon REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 2,188,254 Smithuysen Jan. 23,1940 2,317,241 Ackerman Apr. 20, 1943 2,322,800 Frey June 29, 1943 2,324,755 Beamer July 20, 1943 2,330,206 Dryer Sept. 28, 1943 2,342,124 Danforth Feb. 22, 1944 '2,351,461 Smith June 1'3, 1944 2,378,079 Hays June 12, 

